The present invention relates to an image forming apparatus and a method of determining a transfer voltage to be supplied to a transfer member of the image forming apparatus.
In a conventional image forming device of an electric photography type such as a printer, a copier, and a facsimile, a charge roller charges a surface of a photosensitive drum. An exposure device exposes the photosensitive drum to form a static latent image thereon. A developing device develops the static latent image to form a toner image. A transfer roller transfers the toner image to a sheet as a medium.
A resistance of the transfer roller varies according to an environmental change such as a temperature change and a humidity change, and a change in the transfer roller itself with time. Therefore, it is necessary to adjust a voltage applied to the transfer roller according to such a change.
In a conventional contact-type charge device disclosed in Patent Reference, a specific detection current is supplied to a transfer roller for detecting a resistance of the transfer roller. A transfer voltage to be applied to the transfer roller is determined based on a voltage generated in the transfer roller.
Patent Reference: Japanese Patent Publication No. 11-161057
When a temperature or humidity increases, the resistance of the transfer roller decreases. In the conventional image forming apparatus, when the detection current is supplied to the transfer roller at a high temperature or humidity, the voltage generated in the transfer roller tends to decrease. Accordingly, it is difficult to detect the resistance with high accuracy and determine an optimal transfer voltage based on the resistance.
To this end, it is necessary to increase the detection current. However, when a temperature or humidity decreases, the resistance of the transfer roller increases. In such a case, when the detection current is supplied to the transfer roller at a low temperature or low humidity, a transfer shock may occur in a photosensitive drum.
In view of the problems described above, an object of the present invention is to provide an image forming apparatus, in which it is possible to determine an optimal transfer voltage and prevent a transfer shock from occurring in a photosensitive drum or an image supporting member. Another object of the present invention is to provide a method of determining a transfer voltage to be supplied to a transfer member of the image forming apparatus.
Further objects and advantages of the invention will be apparent from the following description of the invention.